Congenital deafness leads to significant language delays in children acquiring spoken language. Cascading effects of impoverished linguistic knowledge impact a wide range of psychological and cognitive behaviors including self-regulation, working memory, and reading. Cochlear implants (CIs) are a popular treatment option for deaf children. These devices deliver electrical stimulation to the auditory nerve, bypassing malfunctioning peripheral auditory mechanisms. Deaf children who receive cochlear implants early in life and engage in intensive oral/aural therapy often make great strides in spoken language acquisition. However, despite clinicians' best efforts, even under optimal conditions, there is a great deal of variability in language outcomes. The interplay of factors contributing to this lack of success is poorly understood. One mounting concern is that under conditions of deafness, the auditory system may be subject to maladaptive cross-modal plasticity (CMP). In cross-modal plasticity the processing demands of an intact sensory system, such as vision, may recruit nascent auditory cortex making it less available for speech processing. Animal models of deafness have shown evidence of functionally significant cross-modal plasticity with enhancements in visual processing tied to auditory cortical activation. Studies of deaf signing adults have also reported evidence of cross-modal plasticity including visual responsiveness within primary auditory cortex. The specialization of left-hemisphere auditory regions for visual sign language processing attests to the malleability of temporal lobe cortical networks. However, there are significant gaps in our knowledge. The conditions that precipitate CMP and the developmental time course of CMP are not known. There is an urgent need for studies that simultaneously assess auditory and visual processing in deaf children with cochlear implants during the formative stages of language development. Nor is it known how communication modality (signed or speech) impacts cross-modal plasticity. We use electrophysiology to obtain auditory and visual evoked potentials and assess functional integrity and development of the auditory cortex and the presence of cross modal changes in prelingually deaf children who have received cochlear implant. Using innovative behavioral testing and standardized measures of language function we will assess the impact of spoken and signed language experience in the expression of cross-modal plasticity. The proposed studies will advance our understanding of the determinants of CMP and its relation to language use. The findings will have a significant impact on clinical practices for deaf children.